1. Field of the Invention
The invention relates to a ring forming part of a valve assembly, which ring is axially movalbe to control the flow of gas for example within a turbo-machine. The invention further relates to a ring controlling a blow-off opening of a compressor gas turbine plant compressor.
2. Summary of the Prior Art
In gas turbine plant, it is known to include in the compressor, valves arranged in line with one or more stages, and intended to blow-off outwardly part of the air flow, when it is required to operate, on partial loading, for example, outside the design range. By this means so-called "surging" is avoided, surging being the consequence of the fluid flows breaking away from the blades which results in instability of flow.
Conventional blow-off means comprise a plurality of valves distributed over the periphery of the casing and synchronously controlled. These valves must have a substantial section, be able to open and close rapidly, and exhibit good fluid-tightness in the closed position so as not to affect adversely the performance of the engine. These requirements lead to heavy, complex arrangements, with far from negligible overall axial dimensions. Moreover, the opening of such valves can create in the main compressor flow a degree of heterogeneity which can disturb the operation of any downstream compressor.
U.S. Pat. No. 3,057,541 describes a ring blow-off valve cooperating with an opening of corresponding shape. This arrangement makes it possible to reduce the overall size and to simplify control; however, the ring illustrated is a simple blade of limited mechanical strength which is subject to vibration and deformation. Moreover, fluid-tightness is inadequate. The ring slides axially on an annular bearing on the outside of the wall without forming in the closed position a smooth outline of the compressor flow path wall, so that the edges of the blow-off openings bring about flow disturbances.
U.S. Pat. No. 3,588,268 partly remedies these defects by proposing a blow-off ring of U-shaped cross-section, and thus less subject to deformation; moreover, the bearings are inclined thereby ensuring better fluid-tightness. However, this ring is not sufficiently rigid, and also the wall exhibits discontinuity at the blow-off openings thus bringing about flow turbulence. FR-A-No. 2 349 740 discloses a ring-shaped valve, slidably mounted so as to control the opening of an annular slit, but this valve is merely a simple blade which, although it has the advantage of substantially reforming the wall of the fluid flow path in the closed position, suffers, nevertheless, from the same drawbacks as U.S. Pat. No. 3,057,541 when it comes to withstanding vibrations and providing adequate fluid-tightness.
An object of the invention is to provide a valve ring for controlling the flow of gas within a turbo-engine, the structure of which ring valve ensures sufficient rigidity to withstand deformation stresses under various operational conditions.
Another object is to provide an annular device for the blow-off of a compressor, provided with this valve ring, so as to obviate the drawbacks of prior proposals.